U.S. patent application number 13/421486 was filed with the patent office on 2012-07-05 for transparent barrier film and method for producing the same.
This patent application is currently assigned to FRAUNHOFER-GESELLSCHAFT ZUR FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.. Invention is credited to Matthias FAHLAND, John FAHLTEICH, Nicolas SCHILLER, Waldemar SCHOENBERGER, Tobias VOGT.
Application Number | 20120168301 13/421486 |
Document ID | / |
Family ID | 39473954 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120168301 |
Kind Code |
A1 |
FAHLAND; Matthias ; et
al. |
July 5, 2012 |
TRANSPARENT BARRIER FILM AND METHOD FOR PRODUCING THE SAME
Abstract
A transparent barrier film, includes a transparent thermoplastic
film and at least one permeation barrier film. The permeation
barrier film includes a chemical compound of the elements zinc, tin
and oxygen. A mass fraction of zinc is 5% to 70%. Furthermore, a
method is disclosed for the production of a barrier film of this
type.
Inventors: |
FAHLAND; Matthias; (Dresden,
DE) ; VOGT; Tobias; (Kurort Johnsdorf, DE) ;
SCHILLER; Nicolas; (Stolpen OT Helmsdorf, DE) ;
FAHLTEICH; John; (Dresden, DE) ; SCHOENBERGER;
Waldemar; (Dresden, DE) |
Assignee: |
FRAUNHOFER-GESELLSCHAFT ZUR
FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
MUENCHEN
DE
|
Family ID: |
39473954 |
Appl. No.: |
13/421486 |
Filed: |
March 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12597696 |
Oct 26, 2009 |
|
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PCT/EP2008/001694 |
Mar 4, 2008 |
|
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13421486 |
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Current U.S.
Class: |
204/192.15 |
Current CPC
Class: |
C08J 7/06 20130101; C23C
14/0036 20130101; C23C 14/086 20130101; Y10T 428/265 20150115; C08J
2367/02 20130101 |
Class at
Publication: |
204/192.15 |
International
Class: |
C23C 14/35 20060101
C23C014/35 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2007 |
DE |
10 2007 019 994.7 |
Claims
1. A method for producing a transparent barrier film having a
transparent thermoplastic film and at least one permeation barrier
layer, the method comprising: depositing the at least one
permeation barrier layer as a chemical compound of the elements
zinc, tin and oxygen by a vacuum coating process.
2. The method of claim 1, wherein the at least one permeation
barrier layer is deposited with a thickness of 20 nm to 1000
nm.
3. The method of claim 2, wherein the at least one permeation
barrier layer is deposited with a thickness of 50 nm to 300 nm.
4. The method of claim 1, wherein the at least one permeation
barrier layer is deposited by sputtering.
5. The method of claim 4, wherein the sputtering comprises
sputtering a target comprising an alloy of zinc and tin with an
intake of a reactive gas oxygen.
6. The method of claim 5, further comprising controlling an oxygen
inlet by a control loop, in which a controlled variable is
determined from an optical emission spectrum of a sputtering
plasma.
7. The method of claim 6, further comprising determining the
controlled variable as a quotient of an emission line of zinc or
tin and an emission line of an inert gas used.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. patent
application Ser. No. 12/597,696, which is a U.S. National Stage of
International Application No. PCT/EP2008/001694 filed Mar. 4, 2008,
which published as WO 2008/135109 A1 on Nov. 13, 2008, the
disclosure of which is expressly incorporated by reference herein
in its entirety. Further, this application claims priority under 35
U.S.C. .sctn.119 and .sctn.365 of German Application No. 10 2007
019 994.7 filed Apr. 27, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a thermoplastic barrier film with
an excellent permeation barrier to oxygen and water vapor with at
the same time high transparency for light in the visible spectral
range. The invention further relates to a method for producing a
film of this type.
[0004] 2. Background Description
[0005] The use of plastic films as packaging material or as a
protective film for sensitive objects is very widespread. There is
often a requirement that these plastic films not only have to
provide a mechanical protection or a mechanical confinement, but
also at the same time these films should also achieve a blocking
action with respect to gases. This blocking action is also referred
to below as a permeation barrier. With the blocking action of
barrier films, it is often particularly important that this
blocking action is achieved with respect to the oxygen and water
vapor gases contained in the atmosphere. These gases in contact
with objects can cause various chemical reactions, which are often
undesirable with respect to a material to be protected. The use of
barrier films is widespread in the packaging of foodstuffs. The
water vapor transmission rate variable is known as a feature for
the quality of a permeation barrier. For example, a film of
polyethylene terephthalate (PET) with a thickness of 125 .mu.m has
a water vapor transmission rate of approximately 8 g/m.sup.2d
(wherein the "d" in the unit stands for "day" i.e., for 24 hours).
This value is dependent on the thickness of the film. However, in
many applications even much lower permeation values are required.
For example, it is necessary to achieve a value of approximately 1
g/m.sup.2d for food packaging.
[0006] It is known that such values can be achieved if a multilayer
barrier film is used. One ply is hereby the plastic film itself, a
second ply is realized, for example, through a thin layer on the
film which achieves a higher permeation effect. A layer of this
type can be of aluminum, for example. Often a requirement is that a
barrier film must not only have a permeation barrier, but at the
same time it must also still be transparent. Transparency hereby is
defined as a film having a transmission of at least 70% in the
visible spectral range, that is, between 380 nm and 780 nm light
wave length. The requirement for transparency applies in particular
when a barrier film is to be used for the encapsulation of
optoelectronic devices, such as solar cells or display elements.
The combination of a plastic film with a thin metal layer is
unsuitable in the case of this type of requirement.
[0007] It is known that a water vapor transmission rate of
approximately 1 g/m.sup.2d and below can be achieved by a
combination of a plastic film with an oxide layer, wherein the
exact value depends on the coating method used as well as on the
coating material, since the oxides of different elements are not
equally suitable for layers with permeation effect. Thus, it is
known, for example, that a good blocking action cannot be achieved
with TiO.sub.2 layers, whereas oxide layers of the element aluminum
form a very good permeation barrier (N. Schiller et al., Barrier
Coatings on Plastic Web, 44.sup.th Annual Technical Conference
Proceedings, 2001). Furthermore, layers of Si.sub.3N.sub.4 also
have a very good permeation barrier.
[0008] However, the materials Si.sub.3N.sub.4 and aluminum oxide
tend to form cracks after being applied on flexible plastic webs,
which has a negative effect on the barrier effect achieved. The use
of barrier films of this type is likewise restricted thereby. This
fact is not only a disadvantage in the packaging of foodstuffs, but
also when sensitive technical goods are to be protected. Goods of
this type can be, for example, solar cells (requirement: water
vapor transmission rate 10.sup.-3 g/m.sup.2d), thin-film batteries
on a lithium basis (requirement: water vapor transmission rate
2.times.10 g/m.sup.2d) or organic light-emitting diodes
(requirement: water vapor transmission rate 10.sup.-6
g/m.sup.2d).
[0009] Although in general it holds true that the blocking action
of a barrier layer increases with increasing layer thickness, no
further increase in the barrier action can be achieved from a
certain layer thickness due to the crack formation, in particular
with aluminum oxide layers. Thus, for example, with an
Al.sub.2O.sub.3 layer with a layer thickness of approximately 100
nm a value of 0.09 g/m.sup.2d is achieved regarding the barrier
action. With a further increase in layer thickness, a noticeable
increase with respect to the barrier action is no longer
recorded.
[0010] Various improvements have been carried out with known
barrier films. This applies in particular to barrier layers with
increased permeation blocking action. Thus, for example, a
SiO.sub.2 layer with a gradient with respect to the material
properties is known from EP 0 311 432 A2. A mechanical adjustment
of the permeation block to the plastic film and thus a better
mechanical ruggedness are to be achieved therewith.
[0011] Another approach lies in a multilayer structure of a layer
system, in which an inorganic layer and an organic layer are
applied alternately. An approach of this type is presented in J. D.
Affinito et al., Thin Solid Films 290-291 (1996), p. 63-67, wherein
Al.sub.2O.sub.3 is used as an inorganic layer with high blocking
action.
[0012] In DE 10 2004 005 313 A1 an inorganic layer is combined with
a second layer, which is applied in a special magnetron-based PECVD
method. Al.sub.2O.sub.3 as an inorganic layer also forms one of the
possible embodiments in this case.
[0013] All of the known approaches have in common that a high
blocking action is achieved in that at least one material with high
blocking action is deposited on a plastic film by a corresponding
coating technology. However, the materials used thereby, in
particular Al.sub.2O.sub.3, tend to form cracks under mechanical
stress, which limits their use.
SUMMARY OF THE INVENTION
[0014] The technical aim of the invention is therefore to create a
transparent barrier film and a method for the production thereof,
by which the disadvantages of the prior art can be overcome. In
particular, the barrier film is to have very good blocking
properties with respect to oxygen and water vapor and to be less
susceptible to crack formation under mechanical stress.
[0015] The solution to this technical problem is shown by a
transparent barrier film, comprising a transparent thermoplastic
film and at least one permeation barrier layer, characterized in
that the permeation barrier layer comprises a chemical compound of
the elements zinc, tin and oxygen, wherein the mass fraction of
zinc is 5% to 70% and/or a method for producing a transparent
barrier film, comprising a transparent thermoplastic film and at
least one permeation barrier layer, characterized in that the
permeation barrier layer is deposited as a chemical compound of the
elements zinc, tin and oxygen by a vacuum coating process, or the
subject matters with the features of the independent claims.
Further advantageous embodiments of the invention are shown by the
dependent claims.
[0016] A transparent barrier film according to the invention
comprises a transparent thermoplastic film and at least one
permeation barrier layer. The permeation barrier layer thereby
comprises a chemical compound of the elements zinc, tin and oxygen,
wherein the mass fraction of zinc is 5% to 70%.
[0017] It was determined that a thin layer of zinc tin oxide is
present as an amorphous material. It thus has a lower packing
density than comparable microcrystalline materials, such as, for
example, pure zinc oxide. Nevertheless, the mixed oxide of an alloy
of zinc and tin is characterized by a very marked permeation
blocking action. Furthermore, it was surprisingly shown that,
compared to aluminum oxide, layers of zinc tin oxide have a very
much improved flexibility and a lower tendency for cracking. Thus
with an increase in the thickness of a zinc tin oxide layer over
100 nm, it was possible to achieve a further improvement of the
barrier properties.
[0018] A permeation barrier layer of a barrier film according to
the invention can therefore be embodied in a broad layer thickness
range of 20 nm to 1000 nm. However, very good barrier properties
are already achieved in a layer thickness range of 50 nm to 300
nm.
[0019] In addition to a thermoplastic film and a permeation barrier
layer, a barrier film according to the invention can comprise
further layers. Thus, for example, a further layer which comprises
the elements silicon and carbon and has a carbon mass fraction of
1% to 10%, can be deposited between the film and the permeation
barrier layer. A layer of this type serves on the one hand as a
smoothing layer and on the other hand causes an equalization or a
continuous transition of the mechanical properties of the film and
those of the permeation barrier layer.
[0020] However, similar effects can also be achieved without an
intermediate layer of this type, when the permeation barrier layer
on the film is embodied with a gradient such that the permeation
barrier layer on the side facing towards the film has a carbon mass
fraction of up to 5%.
[0021] In another embodiment of the invention, a transparent
barrier film comprises an electrically conductive layer with a
specific resistance of less than 2.times.10.sup.-3 .OMEGA.cm. A
barrier film of this type with a functional layer of this type can
be used at the same time as a transparent electrode. There is also
the possibility that a barrier film according to the invention
comprises a layer stack in which permeation barrier layers,
smoothing layers and/or functional layers are deposited alternately
on a film.
[0022] In a method according to the invention for producing a
transparent barrier film, comprising a transparent thermoplastic
film and at least one permeation barrier layer, the permeation
barrier layer is deposited as a chemical compound of the elements
zinc, tin and oxygen by a vacuum coating process.
[0023] The permeation barrier layer is thereby deposited with a
thickness of 20 nm to 1000 nm and preferably in a range of 50 nm to
300 nm.
[0024] Magnetron sputtering, for example, is suitable as a vacuum
coating method. An alloy of zinc and tin as target is hereby
sputtered, wherein the sputtering process is carried out in the
presence of the reactive gas oxygen.
[0025] In order to be able to achieve uniform barrier properties on
the entire surface of a film, it is also necessary that a
permeation barrier layer with constant layer thickness is deposited
on the entire film surface. The thickness of a deposited permeation
barrier layer can be advantageously adjusted via the supply of the
reactive gas oxygen into the vacuum work chamber. As is known, an
increase in oxygen during a reactive sputtering process leads to an
increased formation of reaction products on the target to be
sputtered, which in turn leads to a reduction in the sputtering
rate. The layer increase of a permeation barrier layer can thus be
adjusted via the supply of the reactive gas.
[0026] In a preferred embodiment the oxygen inlet into the vacuum
work chamber is therefore controlled by a control loop. It is
advantageous hereby in turn if a controlled variable for
controlling the oxygen inlet is determined from the optical
emission spectrum of the sputtering plasma.
[0027] The quotient of an emission line of zinc or tin and an
emission line of the inert gas used, for example, can be determined
as a controlled variable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention is explained in more detail below based on a
preferred exemplary embodiment. The Figs. show:
[0029] FIG. 1 A diagrammatic representation of a control loop for
adjusting the oxygen inflow during reactive deposition of a
ZnSnO.sub.x layer by magnetron sputtering as a function of values
that are obtained from the intensity of two spectral lines of the
magnetron plasma;
[0030] FIG. 2 A graphic representation of the dependence of the
water transmission rate on the layer thickness of a permeation
barrier layer of Al.sub.2O.sub.3 and a permeation blocking layer of
ZnSnO.sub.x.
DETAILED DESCRIPTION OF THE INVENTION
[0031] A permeation barrier layer of zinc tin oxide is deposited on
a thermoplastic plastic film of polyethylene terephthalate (PET) by
a reactive sputtering method. For this purpose a target of a zinc
tin alloy is sputtered in the presence of the inert gas argon and
with the supply of the reactive gas oxygen. It is known that the
degree of the coverage of the target with reaction products, and
thus the deposition rate/layer thickness and the layer composition,
can be adjusted via the supply of the reactive gas oxygen. FIG. 1
shows diagrammatically a control loop by which the permeation
barrier layer can be deposited with a constant layer thickness, and
thus, with constant barrier properties.
[0032] As schematically shown in FIG. 1, in a vacuum chamber 1 for
carrying out the sputtering process, an intensity value of a
spectral line of zinc and an intensity value of a spectral line of
argon are determined by a spectrometer 2, transferred to an
evaluation device 3 and therein a quotient of the two intensity
values is formed. A control signal is produced from the comparison
of the quotient actual value determined in this manner with a
predetermined desired value, which control signal activates an
oxygen inlet valve 4 and readjusts the oxygen supply into the
vacuum chamber 1 such that the determined quotient actual value is
matched to the predetermined desired value.
[0033] In FIG. 2 the permeation blocking action of a barrier film
with a barrier layer of zinc tin oxide, which was deposited
according to the method according to the invention, is shown
graphically as a function of the layer thickness of the barrier
layer. The water vapor transmission rate is thereby plotted on the
y-axis as a measure of the permeation barrier action. The
respective pairs of values with respect to layer thickness and
water vapor transmission rate are shown as small triangles and a
fitted curve resulting therefrom is shown as a dash-dot line.
[0034] The permeation barrier action of a barrier film with
identical film substrate, but an Al.sub.2O.sub.3 layer according to
the prior art is also shown in FIG. 2 as a function of the layer
thickness of the Al.sub.2O.sub.3 layer. The associated pairs of
values are shown as small squares and a fitted curve resulting
therefrom as a dotted line. It can be seen from FIG. 2 that a
barrier film according to the invention with the same thickness has
a better permeation barrier action than a barrier film with an
Al.sub.2O.sub.3 layer according to the prior art. It is likewise
discernible that from a layer thickness of approximately 100 nm no
significant improvement in the blocking action can be achieved with
the Al.sub.2O.sub.3 layer, but with the barrier film according to
the invention an increase in the layer thickness over 100 nm still
causes a significant improvement in the barrier properties, from
which it can be deduced that a barrier film according to the
invention has a lower tendency to cracking than known barrier films
with Al.sub.2O.sub.3 layer.
* * * * *